Simulated dissectible tissue

ABSTRACT

A simulated tissue structure for surgical training is provided. The simulated tissue structure includes a first layer made of silicone and a second layer made of silicone interconnected by a third layer made of polyester fiber that is embedded in part in the first layer and in part in the second layer to create a mechanical linkage between the first layer and the second layer. Part of the third layer that is adjacent to the first layer and part of the third layer that is adjacent to the second layer includes fiber strands coated in silicone. An inclusion that mimics an anatomical structure is located between the first layer and the second layer. The third layer of polyester fibers provides a realistic dissection plane for the practice of the surgical excision of the inclusion.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a continuation application of U.S. application Ser. No. 17/002,033, entitled “Simulated dissectible tissue,” filed Aug. 25, 2020, which is a continuation application of U.S. application Ser. No. 16/431,118, entitled “Simulated dissectible tissue,” filed Jun. 4, 2019, now U.S. Pat. No. 10,755,602, which is a continuation application of U.S. application Ser. No. 15/209,565, entitled “Simulated dissectible tissue,” filed Jul. 13, 2016, now U.S. Pat. No. 10,332,425, which claims the benefit of and is a continuation of International Application Serial No. PCT/US16/41852 entitled “Simulated dissectible tissue” filed on Jul. 12, 2016 which claims priority to and benefit of U.S. Provisional Patent Application Ser. No. 62/193,143 entitled “Simulated dissectible tissue” filed on Jul. 16, 2015 and U.S. Provisional Patent Application Ser. No. 62/257,847 entitled “Simulated dissectible tissue” filed on Nov. 20, 2015 all of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This application is generally related to surgical training tools, and in particular, to simulated tissue structures and models for teaching and practicing various surgical techniques and procedures related but not limited to laparoscopic, endoscopic and minimally invasive surgery.

BACKGROUND OF THE INVENTION

Medical students as well as experienced doctors learning new surgical techniques must undergo extensive training before they are qualified to perform surgery on human patients. The training must teach proper techniques employing various medical devices for cutting, penetrating, clamping, grasping, stapling, cauterizing and suturing a variety of tissue types. The range of possibilities that a trainee may encounter is great. For example, different organs and patient anatomies and diseases are presented. The thickness and consistency of the various tissue layers will also vary from one part of the body to the next and from one patient to another. Different procedures demand different skills. Furthermore, the trainee must practice techniques in various anatomical environs that are influenced by factors such as the size and condition of the patient, the adjacent anatomical landscape and the types of targeted tissues and whether they are readily accessible or relatively inaccessible.

Numerous teaching aids, trainers, simulators and model organs are available for one or more aspects of surgical training. However, there is a need for models or simulated tissue elements that are likely to be encountered in and that can be used for practicing endoscopic and laparoscopic, minimally invasive, transluminal surgical procedures. In laparoscopic surgery, a trocar or cannula is inserted to access a body cavity and to create a channel for the insertion of a camera such as a laparoscope. The camera provides a live video feed capturing images that are then displayed to the surgeon on one or more monitors. At least one additional small incision is made through which another trocar/cannula is inserted to create a pathway through which surgical instruments can be passed for performing procedures observed on the video monitor. The targeted tissue location such as the abdomen is typically enlarged by delivering carbon dioxide gas to insufflate the body cavity and create a working space large enough to accommodate the scope and instruments used by the surgeon. The insufflation pressure in the tissue cavity is maintained by using specialized trocars. Laparoscopic surgery offers a number of advantages when compared with an open procedure. These advantages include reduced pain, reduced blood and shorter recovery times due to smaller incisions.

Laparoscopic or endoscopic minimally invasive surgery requires an increased level of skill compared to open surgery because the target tissue is not directly observed by the clinician. The target tissue is observed on monitors displaying a portion of the surgical site that is accessed through a small opening. Therefore, clinicians need to practice visually determining tissue planes, three-dimensional depth perception on a two-dimensional viewing screen, hand-to-hand transfer of instruments, suturing, precision cutting and tissue and instrument manipulation. Typically, models simulating a particular anatomy or procedure are placed in a simulated pelvic trainer where the anatomical model is obscured from direct visualization by the practitioner. Ports in the trainer are employed for passing instruments to practice techniques on the anatomical model hidden from direct visualization. Simulated pelvic trainers provide a functional, inexpensive and practical means to train surgeons and residents the basic skills and typical techniques used in laparoscopic surgery such as grasping, manipulating, cutting, tying knots, suturing, stapling, cauterizing as well as how to perform specific surgical procedures that utilized these basic skills.

Organ models for use with simulated pelvic trainers on which surgeons can train surgical techniques are needed. These organ models need to be realistic so that the surgeon can properly learn the techniques and improve their skills. Currently, most simulated tissue structures are made of silicone. On the one hand, silicone is very elastic and when cut and silicone rebounds quickly. On the other hand, real tissue does not rebound fully when manipulated. Furthermore, silicone will tear fairly easily in the presence of a cut or a hole, but it resists tearing if there are no defects present. On the other hand, real tissue dissects easily. Also, adhering tissue surfaces poses further difficulties, such as excessive tackiness, when desiring a realistic interface. Therefore, challenges exist to making simulated tissue structures out of silicone that not only appear real, but also, function with the feel of real tissue when dissected and manipulated surgically. The present invention provides such a simulated tissue structure.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a simulated tissue structure for surgical training is provided. The simulated tissue structure includes a first layer of silicone polymer having a configuration of a planar sheet with an upper surface and a lower surface defining a thickness therebetween. The simulated tissue structure includes a second layer of silicone polymer having a configuration of a planar sheet with an upper surface and lower surface defining a thickness therebetween. The second layer is spaced apart from the first layer such that the upper surface of the first layer faces the lower surface of the second layer. The simulated tissue structure includes a third layer made of a plurality of entangled fibers located between the first layer and the second layer. At least part of the plurality of entangled fiber filaments of the third layer are embedded in at least one of the first layer and second layer.

According to another aspect of the invention, a simulated tissue structure for surgical training is provided. The simulated tissue structure includes a first layer of silicone polymer with an upper surface and a lower surface. The simulated tissue structure includes a second layer of silicone polymer with an upper surface and lower surface. The second layer is spaced apart from the first layer such that the upper surface of the first layer faces the lower surface of the second layer. The simulated tissue structure further includes a third layer made of a plurality of entangled fiber filaments located between the first layer and the second layer. The third layer has an upper surface and a lower surface. At least part of the lower surface of the third layer is embedded in the upper surface of the first layer. The simulated tissue structure includes a fourth layer made of a plurality of entangled fiber filaments located between the first layer and the second layer. The fourth layer being embedded in the second layer at the lower surface of the second layer. The simulated tissue structure includes a first inclusion located between the third layer and the fourth layer.

According to another aspect of the invention, a simulated tissue structure for surgical training is provided. The simulated tissue structure includes a first tube defining a first lumen. The first tube has an inner layer, an outer layer and a middle layer. The outer layer is connected to the inner layer by the middle layer. The middle layer is made of a plurality of entangled fibers embedded in part in the inner layer and in part embedded in the outer layer. The simulated tissue structure further includes a second tube defining a second lumen. The second tube has an outer layer and an inner layer. The first tube is located inside the second lumen. The simulated tissue structure further includes an inclusion located between the inner layer of the second tube and the outer layer of the first tube.

According to another aspect of the invention, a simulated tissue structure for surgical training is provided. The simulated tissue structure includes a first layer made of silicone and a second layer made of silicone interconnected by a third layer made of polyester fiber that is embedded in part in the first layer and in part in the second layer to create a mechanical linkage between the first layer and the second layer. Part of the third layer that is adjacent to the first layer and part of the third layer that is adjacent to the second layer includes fiber strands coated in silicone. An inclusion that mimics an anatomical structure is located between the first layer and the second layer. The third layer of polyester fibers provides a realistic dissection plane for the practice of the surgical excision of the inclusion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational cross-section of a simulated tissue structure according to the present invention.

FIG. 2A is top perspective view of a casting dish according to the present invention.

FIG. 2B is a top perspective view of a casting dish and a first layer of silicone according to the present invention.

FIG. 2C is a top perspective view of a casting dish, first layer of silicone and fiber layer according to the present invention.

FIG. 3A is a top perspective view of an organ model made with a simulated tissue structure according to the present invention.

FIG. 3B is a top perspective view of an organ model made with a simulated tissue structure according to the present invention.

FIG. 3C is a top perspective, sectional view of an organ model made with a simulated tissue structure according to the present invention.

FIG. 4 is a top perspective, sectional view of an organ model made with simulated tissue structure according to the present invention.

FIG. 5 is a top perspective view of a surgical training device according to the present invention.

FIG. 6 is an exploded view of a simulated rectum model according to the present invention.

FIG. 7 is a cross-sectional view of a simulated rectum model according to the present invention.

FIG. 8 is a sectional view of a cross-section of a simulated rectum model according to the present invention.

FIG. 9A is cross-sectional view of a casting dish, a first layer of silicone and a first layer of fiber according to the present invention.

FIG. 9B is a cross-sectional view of the first layer of silicone and first layer of fiber of FIG. 9A located above a casting dish, a second layer of silicone, a second layer of fiber and simulated vessels according to the present invention.

FIG. 10A is a top view of a casting dish according to the present invention.

FIG. 10B is a side elevational view of the casting dish of FIG. 10A according to the present invention.

FIG. 11A is a side elevational view of a casting dish, a layer of wet foam and a layer of fiber according to the present invention.

FIG. 11B is a side elevational view of the first layer of fiber and layer of foam from FIG. 11A located above a second layer of silicone according to the present invention.

FIG. 11C is a side elevational view of the first layer of fiber and layer of foam and second layer of silicone of FIG. 11B located beneath a second layer of fiber, third layer of silicone and artificial vessels according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A simulated tissue structure 30 according to the present invention is shown in FIG. 1 . The structure 30 includes a first layer 32 and a second layer 34 having an upper surface 36, 38 and lower surface 40, 42, respectively. The first layer 32 and the second layer 34 are interconnected by a third layer 44 defining a gap 46 therebetween. The simulated tissue structure 30 may further optionally include inclusions 48 located between the first and second layers 32, 34. The inclusions 48 include simulated vessels, veins, tumors, ducts, vasculature, nerves, fat deposits, pathologies or other anatomical structures. The inclusions 48 are typically made of silicone but may also be made of other polymers or other suitable material and realistically shaped, colored and configured.

The third layer 44 comprises a plurality of one or more non-aligned, randomly arranged, nonwoven fiber 50 connected to the first layer 32 and/or second layer 34 at one or more location along the length of the fiber(s) 50. The fiber 50 is connected to one or more of the first layer 32 and the second layer 34 by being embedded into the one or more of the first layer 32 and the second layer 34 during the manufacturing process which will be described in greater detail below. Each fiber may be in the form of a strand, filament, yarn, micro-fiber and the like and has a length and a first free end and a second free end. Adhesive is not used to connect the fiber. The fiber of the third layer 44 is resident within the gap 46 in a randomly arranged fashion. One strand of fiber 50 may be connected to the first layer 32 at one location and then connected to the first layer 32 again at another location along the length of the fiber or to the second layer 34 and its free ends may or may not be embedded in the first or second layer. Some strands of fiber 50 may not be connected to the first layer 32 or second layer 34 and are freely disposed between the first layer 32 and the second layer 34. Some strands of fiber 50 are entangled and intertwined with other strands in a loose fashion such that the strands may move relative to other strands. The fiber may span the gap 46 to be connected to the opposite or second layer 34 at one or more location along the length of the fiber. It is possible to use a single fiber strand instead of a plurality of fiber strands to comprise the third layer 44. The single fiber strand would be longer in length to fill and create a gap 46 between the layers 32, 34 compared to the use of shorter strands to fill the same gap. The fibers are selected from any suitable material such as polyester, polyamide, acrylic, acetate, polyolefin, cotton, fiberfill, batting, polyethylene terephthalate, polyethylene naphthalate, nylon, polyfill, fiberfill, polymer, plastic, spandex or other suitable fiber, natural fiber, non-absorbent fiber, synthetic fiber or fiber-like material. The material may be woven, not woven or partially woven. Fiberfill is typically made by garnetting in which a garnet machine takes fibers and combs them into a batt form. The garnet machine may then fold and chop the fibers to make strands that are shorter and clumped together. The fibers mat together entangle and bunch.

One or more of the first layer 32 and second layer 34 has a substantially uniform thickness between its upper surface 36, 38 and its lower surface 40, 42 defining a substantially planar configuration. In one variation, the first layer 32 and the second layer 34 have a substantially uniform thickness between its upper surface 36, 38 and its lower surface 40, 42. The lower surface 42 of the second layer 34 faces the upper surface 36 of the first layer 32. In the location where the fibers 50 are attached to one of the first layer 32 and second layer 34, the layer 32, 34 has a reduced thickness because part of the thickness is taken by the thickness of the fiber itself. The first and second layers 32, 34 are made of any suitable elastomeric material such as silicone. Room temperature vulcanization silicone is used in one variation. In one variation, the second layer 34 is avoided and the simulated tissue structure 30 includes only the first layer 32 and the third layer 44 of fiber connected to the first layer 32.

The method of manufacturing the simulated tissue structure 30 will now be described with reference to FIGS. 2A-2C. A casting dish 52 having a textured surface 54 is provided. In another variation, the casting dish 52 has a smooth surface. Uncured room temperature vulcanization silicone is provided and applied evenly onto the textured surface 54 of the casting dish 52 as shown in FIG. 2B to form a thin first layer 32. A spatula may be used to calendar the silicone evenly into a thin first layer 32. While the silicone of the first layer 32 is in an uncured state, the third layer 44 is applied. In particular, a layer of polyester fibers 50 is placed onto the upper surface 36 of the first layer 32 while the first layer 32 is still wet. The polyester fibers 50 are arranged in a desired shape, thickness and density. The fibers 50 are then tamped down into the first layer 32 to help embed the fibers into the first layer 32 in a random fashion. Some parts of the fibers 50 are embedded in the silicone and most are exposed to the air and remain available to embed in a subsequent silicone casting.

Any optional inclusions 48 are placed onto or in juxtaposition with the upper surface 36 of the first layer 32. The inclusions 48 are placed before the polyester fibers 50 are applied. In another variation, the inclusions 48 are placed after the polyester fibers 50 are applied. If the inclusions 48 are placed before the polyester fibers 50, the inclusions 48 will become adhered to the first layer 32 as the silicone cures. If the inclusions 48 are placed after the polyester fibers 50, only portions of the inclusions 48 that are in direct contact with the wet silicone of the first layer 32 will become adhered to the first layer 32 as the silicone cures. Thereby, the inclusions may be selectively adhered to either the first layer and/or the second layer to provide a realistic scenario for practicing the removal of an inclusion in a simulated surgical excision of the inclusion 48 with the surgeon employing careful and selective dissection. Also, only portions of the fibers 50 that are in contact with the wet silicone of the first layer 32 will become adhered to the first layer 32. The silicone of the first layer 32 is allowed to cure fully embedding parts of the fibers into the first layer 32. In one variation, the inclusions 48 are placed onto the first layer 32 after the first layer 32 has cured, thereby, not being embedded therein. Similarly, the fiber third layer 44 is placed onto a cured first layer 32 and, thereby, not becoming bonded thereto.

After the first layer 32 is cured, the textured first layer 32 is removed from the casting dish 52. Typically, very thin sheets of silicone are difficult to remove from a casting dish 52 even with a layer of mold release coating the casting dish. However, the presence of fibers 50 that are attached to the first layer 32 upon curing of the silicone enable extremely thin layers of silicone to be removed from a casting dish without resulting in the layer tearing or being damaged. The interconnected embedded fibers 50 help to gently pull the thin layer away from the casting dish. Hence, the fiber layer 44 makes the tissue structure 30 more resilient to tearing and advantageously enables extremely thin layers of silicone to be casted and safely removed without tearing from the casting dish. The textured casting dish 52 advantageously provides locations of reduced thickness as wet silicone will pool in the locations where the casting dish is deeper. In one variation, the texture of casting dish 52 creates a multitude of small holes throughout the layer. The holes are relatively unrecognizable because advantageously the fiber layer provides a visual of glistening tissue as light is reflected in many directions from the shiny fiber mimicking wet live tissue. Furthermore, the holes act as points of origin for tears in the first layer 32 of silicone which is advantageous for simulating dissection, because, as mentioned previously, defects in the silicone help overcome the large and often unrealistic resistance to tearing of silicone. However, as the first layer 32 of silicone is made thinner, it become more difficult to de-mold and remove. The added fibers 50, which are placed on top of the uncured silicone while in the casting dish 52, form a composite with the silicone and make it possible to de-mold extremely thin sheets. Furthermore, advantageously, the presence of fibers 50 atop and in connection with the first layer 32 while the silicone of the first layer 32 is still uncured creates a capillary action or absorbency depending upon the type of material used in making the fiber that pulls silicone into the fibers 50 and away from the casting dish 52. This capillary action results in extremely thin spots and even small holes in the casting of the first and second layers 32, 34 which are easy and realistic to dissect using surgical instruments. This capillary action allows for the formation of sheets on un-textured, smooth casting dishes with the same desirable end results wherein the layers 32, 34 have locations of reduced thickness of silicone. The isolated spots of reduced thickness in the silicone layer 32, 34 act as points of origin for tears that mimic real dissection with a scalpel. The capillary-like action takes place when the fibers 50 are placed on the silicone when it is in an uncured state and results in at least part of the fiber strand becoming coated with the polymer or silicone polymer. The silicone bonds well to the micro-fibers and advantageously reduces friction when the fibers are moved against each other creating a slick, almost wet-like interface. In one variation, all of the fibers are coated before being embedded in one or more of the first and second layers. The fibers 50 of the third layer 44 are not ordered or aligned but randomly tangled. This tangled configuration resist the silicone's natural rebound, greatly enhancing the realistic feel of the tissue structure 30, especially when performing blunt dissection as in laparoscopic surgery, as the fibers can slide/move relative to each other dampening the resiliency of the silicone. Also, the tangled configuration of the fibers 50 make separation of the first layer 32 and the second layer 34 a function of pulling tangled fibers instead of pulling layers that are adhered with silicone or other adhesive. In a sense, the fibers act as an adhesive layer or mechanical linkage between the first layer 32 and the second layer 34. The adhesion being defined by the tangled fibers of the third layer 44 and the degree of their adhesion to the layers 32, 34. Separating the tangled fibers when pulling the first and second layers apart permits the surgeon to employ and practice respect for tissue techniques instead of using larger forces merely because the model is made of silicone, with adjoining layers firmly adhered with adhesive and the like. Therefore, the present invention is highly effective for making dissectible tissue models.

The method of manufacturing the simulated tissue structure 30 includes providing a second layer 34 of silicone. The second layer 34 of silicone is applied to a smooth or textured casting dish to create a thin layer of silicone. A spatula may be used to calendar the silicone evenly into a thin second layer 34. While the silicone of the second layer 34 is in an uncured state, the combination of the first layer 32 and the third layer 44 previously made is applied onto the lower surface 42 of the second layer 34 while the silicone of the second layer 34 is in an uncured state. In particular, the third layer 44 of polyester fibers 50 is placed onto the lower surface 42 of the second layer 34. The fibers 50 are then tamped down onto the second layer 34 to help embed the fibers 50 into the second layer 34. Any optional inclusions 48 are may be optionally provided onto the lower surface 42 of the second layer 32. The inclusions 48 are placed before the polyester fibers 50 are applied. The inclusions 48 together with the fiber layer may become adhered to the second layer 34 as the silicone cures. In one variation, the second layer 34 is allowed to cure before the first layer 32 and third layer 44 are overlaid onto the second layer 34 if adhesion of fiber only to the first layer 32 is desired.

In one variation, a frame is provided having a central window of a desired shape. The frame (not shown) is applied against the lower surface 40 of the first layer 32 and pressed down toward the second layer 34 to bring the perimeter of the first layer 32 into sealing contact with the uncured silicone of the second layer 34 capturing the third layer 44 in between creating a pocket of fibers 50 with or without inclusions 48. The perimeter areas of the first and second layers 32, 34 are without fibers, in one variation, ensuring that the first and second layers 32, 34 come into direct contact with each other to create and substantially seal the pocket. In another variation, the pocket is not created and the sides of the simulated tissue structure 30 are left open as shown in FIG. 1 . The silicone of the second layer 34 is allowed to cure fully resulting in the third layer being attached and embedded in the upper surface 36 of the first layer 32 and the lower surface 42 of the second layer 34 in sandwich-like fashion. One of the first layer 32 and second layer 34 may have a greater thickness than the other. In another variation, both the first layer 32 and the second layer 34 have the same thickness.

The most basic variation of the simulated tissue structure 30 is a first layer 32 sheet of silicone with fibers 50 on one side. This basic variation can be combined with other processes to create models of increasing complexity having additional layers of silicone, fiber and inclusions provided on outer or inner surfaces. After the first layer 32 of silicone with fibers 50 added to one side is cured and removed from the casting dish 52, the second layer 34 of silicone can be applied to the same casting dish 52 and the previously made first layer 32 together with attached third layer 44 can be placed fiber-side down onto the uncured second layer 34. This results in a sandwich with thin sheets of silicone on the exterior and micro fibers and inclusions in the interior having various degrees and locations of being embedded and/or adhesion. This assembly can then be used alone or as a component to a larger and more complex model. The thickness of the first and second layers is approximately between 1.0 millimeter and 7.0 millimeters and, preferably, between 0.5 millimeters and 3 millimeters. The third layer is approximately between 2.5 millimeters to 25.0 millimeters.

An example of the simulated tissue structure 30 being employed in a larger model is shown in FIGS. 3A-3C. FIGS. 3A-3C illustrates a pelvic model 56 with the simulated tissue structure 30 of the present invention. The pelvic model 56 includes a portion of a simulated pelvis 58. The simulated tissue structure 30 includes only a first layer 32 and a third layer 44 of fibers 50 without a second layer 34 of silicone. The upper surface 36 of the first layer 32 faces toward the simulated pelvis 58 such that the fibers 50 are located between the first layer 32 and the simulated pelvis. The simulated pelvis 58 serves as an armature on which the simulated tissue structure of the present invention is attached. The simulated tissue structure 30 of the present invention is placed over the simulated pelvis 58 that is shown to include other anatomical features including but not limited to ducts 59 and a defect 60 interior to the first layer 32. The edges of the first layer 32 are adhered to the backside of the simulated pelvis 58 as shown in FIG. 3B and optionally at other selected areas along the first layer 32. When the pelvic model 56 is approached by a surgeon employing a laparoscope, the lower surface 40 of the first layer 32 will be visualized first. Because of the textured surface of the first layer 32 and because of the varying placement and arrangement of the third layer 44 beneath the thin first layer 32, the model 56 will appear more realistic than a uniform layer of silicone without texturing or without the underlying fiber layer 44. If simulated anatomical structures and/or inclusions 48 are employed, the fiber layer 44 will advantageously serve to obscure portions of the structures/inclusions making them more difficult to discern making the dissection practice more realistic and difficult for the practitioner. Thicker areas of the third layer 44 from having more fiber will obscure underlying structures/inclusions 48 more than thinner areas of the third layer 44 having less fiber thickness. Also, the first layer 32 may vary in thickness itself permitting different degrees of visualization of the underlying structures/tissues. The first layer 32 may be dyed red or pink. The light-colored or white fibers 50 will make the overlaying first layer 32 appear lighter in color in certain locations. With the underlying third layer 44 of fiber, the first layer 32 will appear lighter red or lighter pink in certain areas relative to other locations where there is no fiber or less fiber. The surgeon will then practice making an incision 62 with a scalpel or a blunt surgical instrument. An incision 62 is shown in FIGS. 3A and 3C. Upon making the incision 62, the first layer 32 will not rebound due to the elasticity of the silicone itself which would resulting in the incision 62 appearing to close at an unrealistically fast rate or response. Instead, the incision 62 will remain substantially open as shown as a result of the fiber layer 44 dampening or holding back resiliency of the silicone itself. Also, the ability to mold very thin layers of silicone with the help of the fiber layer, the resulting thinner layer of silicone will have less thickness and reboundability. Under laparoscopic observation, the polyester fibers 50 appear to glisten as the fibers 50 reflect light in various directions advantageously making the simulated tissue structure 30 appear wet or moist as real tissue without the help of any liquid being present in the model. In laparoscopic simulations, the simulated tissue structures may appear unrealistic outside of a simulator or outside of a laparoscopic simulation environment and when observed with the naked eye, but because visualization takes place via a scope in a cavernous trainer that is artificially illuminated, certain liberties can be taken to achieve realistic advantages that could not be achieved for organs suitable for open procedures used outside the a laparoscopic simulation environment. In essence, the fibers 50 of the third layer 44 may appear very unrealistic as an organ or tissue simulation when observed with the naked eye but appear and behave very realistically in a laparoscopic training environment which will be described in greater detail below. After the incision 62 is made, the inclusions 48 including the ducts 59 and underlying artificial tissue structures 60 are exposed.

Turning now to FIG. 4 , there is shown another example in which the simulated tissue structure 30 of the present invention is employed in an organ model. FIG. 4 illustrates an abdominal organ model 64 that includes simulated bowels 66 atop a simulated mesentery or omentum layer 68 that comprises the simulated tissue structure 30 according to the present invention. The bottom surface 40 of the structure 30 is facing up and vasculature 70 is included as an inclusion 48 attached to the first layer 32. The vasculature 70 was attached to the first layer 32 before the third layer 44 of fiber 50 was embedded. Hence, the vasculature is clearly visible through the first layer 32. The simulated mesentery layer 68 is made of silicone that is dyed yellow and the vasculature is red in color and made of silicone.

Although a method of forming a substantially flat or pocket-like simulated tissue structure 30 was described previously hereinabove, a method of forming a tubular-shaped simulated tissue structure 30 according to the present invention will now be described. Uncured silicone is provided and applied evenly to a rotating mandrel to create the first layer 32. While the silicone of the first layer 32 is still wet, the polyester fiber layer is applied to form a third layer 44 of fibers 50. The fibers may be randomly or evenly applied or strategically applied forming areas where more or less fiber is intentionally located to effect a desired simulation outcome. The first layer 32 of silicone is allowed to cure to embed the fibers 50 into the first layer 32. The cured first layer 32 is taken off the mandrel and has a cylindrical shape with the lower surface 40 of the first layer 32 forming the interior of the cylinder and defining the cylinder lumen. The cylindrical shape of the first layer 32 and the third layer 44 may be inverted to place the fiber layer 44 inwardly and the lower surface 40 of the first layer 32 forming a smooth outer surface of the cylinder. Inclusions 48 may be applied to the outer surface of the cylinder either after inversion or prior to forming the first layer 32. In another variation, the cylinder is not inverted. A first strip of uncured silicone is applied onto a surface. The first strip has a length approximately equal to the length of the tubular first layer 32. The tubular first layer 32 and third layer 44 is aligned with the first strip and laid down onto the first strip with the fiber side of the combination facing the uncured first strip and tamped down to embed fibers 50 into the first strip. The first strip is allowed to cure to embed the fibers 50 of the third layer 44 into the first strip. A second strip of uncured silicone is applied to a surface. The second strip has a length approximately equal to the length of the tubular first layer 32. The tubular first layer 32, third layer 44 and first strip is laid onto the second strip while the silicone of the second strip is still wet to embed the fibers 50 of the third layer 44. The tubular first layer 32 is applied to the second strip offset from the first strip so that an adjacent portion of exposed fibers of the third layer 44 come in contact with the wet second strip, preferably adjacent to the first strip and slightly overlaying the first strip to form an almost continuous second layer 34. This process is repeated to form the second layer 34 from a plurality or any number of silicone sections or strips. The strips may be rectangular, triangular or any other shape to suitably cover the cylindrical surface and embed the third layer into the second layer 34. Different organ models such as bowels can be formed with the simulated tissue structure 30 having a tubular shape and any inclusions 48 can be provided directly to either side of the first layer 32 prior to the application of the fiber layer 44 or after the fiber layer 44 or directly to the second layer 34. In another variation, the second layer 34 is not applied and the simulated tissue structure includes the first and second third layer and any inclusions 48.

In another variation, the simulated tissue structure 30 by itself or formed as part of another larger model or tissue structure such as the abdominal organ model 64 or pelvic model 56 described above with respect to FIGS. 3A-3C and FIG. 4 is sized and configured to be placed inside a simulated laparoscopic environment such as a surgical training device 10 of the like shown in FIG. 5 . Of course, the simulated tissue structure may also be used to practice open surgical procedures.

A surgical training device 10 that is configured to mimic the torso of a patient such as the abdominal region is shown in FIG. 5 . The surgical training device 10 provides a body cavity 12 substantially obscured from the user for receiving simulated or live tissue or model organs or training models of the like described in this invention. The body cavity 12 is accessed via a tissue simulation region 14 that is penetrated by the user employing devices to practice surgical techniques on the tissue or practice model found located in the body cavity 12. Although the body cavity 12 is shown to be accessible through a tissue simulation region, a hand-assisted access device or single-site port device may be alternatively employed to access the body cavity 12. An exemplary surgical training device is described in U.S. patent application Ser. No. 13/248,449 entitled “Portable Laparoscopic Trainer” filed on Sep. 29, 2011 and incorporated herein by reference in its entirety. The surgical training device 10 is particularly well suited for practicing laparoscopic or other minimally invasive surgical procedures.

Still referencing FIG. 5 , the surgical training device 10 includes a top cover 16 connected to and spaced apart from a base 18 by at least one leg 20. FIG. 5 shows a plurality of legs 20. The surgical training device 10 is configured to mimic the torso of a patient such as the abdominal region. The top cover 16 is representative of the anterior surface of the patient and the space 12 between the top cover 16 and the base 18 is representative of an interior of the patient or body cavity where organs reside. The surgical trainer 10 is a useful tool for teaching, practicing and demonstrating various surgical procedures and their related instruments in simulation of a patient undergoing a surgical procedure. Surgical instruments are inserted into the cavity 12 through the tissue simulation region 14 as well as through pre-established apertures 22 in the top cover 16. Various tools and techniques may be used to penetrate the top cover 16 to perform mock procedures on simulated organs or practice models placed between the top cover 16 and the base 18. The base 18 includes a model-receiving area 24 or tray for staging or holding a simulated tissue model or live tissue. The model-receiving area 24 of the base 18 includes frame-like elements for holding the model (not shown) in place. To help retain a simulated tissue model or live organs on the base 18, a clip attached to a retractable wire is provided at locations 26. The retractable wire is extended and then clipped to hold the tissue model in position substantially beneath the tissue simulation region 14. Other means for retaining the tissue model include a patch of hook-and-loop type fastening material affixed to the base 18 in the model receiving area 24 such that it is removably connectable to a complementary piece of hook-and-loop type fastening material affixed to the model.

A video display monitor 28 that is hinged to the top cover 16 is shown in a closed orientation in FIG. 5 . The video monitor 28 is connectable to a variety of visual systems for delivering an image to the monitor. For example, a laparoscope inserted through one of the pre-established apertures 22 or a webcam located in the cavity and used to observe the simulated procedure can be connected to the video monitor 28 and/or a mobile computing device to provide an image to the user. Also, audio recording or delivery means may also be provided and integrated with the trainer 10 to provide audio and visual capabilities. Means for connecting a portable memory storage device such as a flash drive, smart phone, digital audio or video player, or other digital mobile device is also provided, to record training procedures and/or play back pre-recorded videos on the monitor for demonstration purposes. Of course, connection means for providing an audio visual output to a screen larger than the monitor is provided. In another variation, the top cover 16 does not include a video display but includes means for connecting with a laptop computer, a mobile digital device or tablet and connecting it by wire or wirelessly to the trainer.

When assembled, the top cover 16 is positioned directly above the base 18 with the legs 20 located substantially around the periphery and interconnected between the top cover 16 and base 18. The top cover 16 and base 18 are substantially the same shape and size and have substantially the same peripheral outline. The internal cavity is partially or entirely obscured from view. In the variation shown in FIG. 5 , the legs include openings to allow ambient light to illuminate the internal cavity as much as possible and also to advantageously provide as much weight reduction as possible for convenient portability. The top cover 16 is removable from the legs 20 which in turn are removable or collapsible via hinges or the like with respect to the base 18. Therefore, the unassembled trainer 10 has a reduced height that makes for easier portability. In essence, the surgical trainer 10 provides a simulated body cavity 12 that is obscured from the user. The body cavity 12 is configured to receive at least one surgical model accessible via at least one tissue simulation region 14 and/or apertures 22 in the top cover 16 through which the user may access the models to practice laparoscopic or endoscopic minimally invasive surgical techniques.

Turning now to FIGS. 6-8 , a simulated rectum model 100 comprising a composite of simulated tissue structures 30 will now be described. The simulated rectum model 100 includes a first tube 102 made of silicone. The first tube 102 may include an embedded mesh material such that the first tube 102 is capable of retaining sutures such that they do not pull out or tear through the silicone. The first tube 102 defines a first lumen 103 extending between a proximal end and a distal end.

The simulated rectum model 100 further includes a second tube 104 defining a second lumen 105 and extending between a proximal end and a distal end. The second tube 104 is made of yellow urethane foam. A layer of foam is formed and then folded into a cylindrical shape and the ends adhered to form a tube. The anterior end of the urethane foam second tube 104 is thinner as shown in FIG. 6 . The second lumen 105 is dimensioned to receive the first tube 102 inside the second lumen 105 in a concentric-like fashion. The second tube 104 is adhered to the first tube 102 using cyanoacrylate glue.

The model 100 further includes a third tube 106. The third tube 106 is simulated tissue structure 30 of the like described above having a first layer 32, a second layer 34 and a third layer 44 of polyfill fiber 50 that is formed into a cylindrical tube to define a third lumen 107. The first layer 32 of the third tube 106 is yellow in color and the second layer 34 is white in color. The third layer 44 is made of white polyfill fiber. The diameter of the third lumen 107 is dimensioned to receive the second tube 104 inside the third lumen 107 in an eccentric fashion. The third tube 106 is adhered to the second tube 104 with adhesive such as cyanoacrylate glue.

The simulated rectum model 100 further includes a fourth tube 108. The fourth tube 108 is simulated tissue structure 30 of the like described above having a first layer 32 and a third layer 44 of polyfill fiber 50 but does not have a second layer 34 that is formed into a cylindrical tube to define a fourth lumen 109 such that the third layer 44 of free polyfill fibers faces the fourth lumen 109. The second layer 34 is pink in color. The third layer 44 is made of white polyfill fiber. In one variation, the fourth tube 108 includes a second layer 34 that is white in color. The diameter of the fourth lumen 109 is dimensioned to receive the third tube 106 inside the fourth lumen 109 in a concentric-like fashion. The fourth tube 108 is adhered to the third tube 106 with adhesive in select areas.

The simulated rectum model 100 further includes a simulated prostate system 110 located between the third tube 106 and the fourth tube 108. The simulated prostate system 110 is located at the anterior side of the model 100. The simulated prostate system 110 includes a simulated prostate, simulated seminal vesicles, simulated bladder, simulated urethra, and simulated vas deferens. The simulated urethra and simulated vas deferens are made of silicone formed into a solid tube. The simulated seminal vesicles are made of urethane foam over molded onto the simulated vas deferens. The simulated prostate is made of urethane foam over molded onto the simulated urethra.

The simulated rectum model 100 further includes additional polyfill material located between the fourth tube 108 and the third tube 106 at the anterior side of the model 100 and surrounding the simulated prostate system 110.

The simulated rectum model 100 is fantastically suited for practicing transanal total mesorectal excision (TaTME) for cancer located in the lower rectum. In such a surgical procedure the cancerous simulated rectum is approached through the anus via a sealable port connected to a channel that is inserted into the simulated rectum. A purse-string suture seals off the cancerous portion of the rectum. The purse-string suture is a type of suture technique that the user of the model 100 can practice. It involves suturing around the circumference of the rectum and pulling it tight to seal off the area of the rectum that includes the tumor. The first tube 102 includes mesh embedded in the silicone layer of the tube to hold the purse-string suture in place. The silicone layer of the first tube 102 allows the purse-string suture to be pulled tight. Then, the surgeon will cut down posteriorly through the second tube 104 which represents the mesorectum. The surgeon will continue to dissect through the first layer 32 of the third tube 106 and then dissect circumferentially around in the third layer 44 of the third tube 106 being careful not to penetrate the second layer 34 of the third tube 106 because doing so would endanger the adjacent simulated prostate system 110. The first layer 32 of the third tube 106 is yellow, which is the same color as the simulated mesorectum, second tube 104, making it hard to distinguish apart from the second tube 104. While dissecting circumferentially around in the third layer 44, care must be taken not to penetrate the second layer 34, because the third layer 44 is made of white polyfill and the second layer 34 is made of white silicone making them difficult to distinguish, thereby, teaching the practitioner to exercise due care. The fourth tube 108, and in particular, the second layer 34 of the fourth tube 108 is red, representing the muscle and the pelvic floor. Accidental dissection into the second layer 34 of the fourth tube 108 and circumferential progression of dissection in this location would possibly lead to intersection with the simulated prostate system 110 which this model 100 teaches the surgeon to avoid. Dissection within the third layer 44 of the third tube 106 leads to a safe excision of the simulated prostate system 110. After dissecting posteriorly, anterior dissection begins by dissecting through the thinner section of the simulated mesorectum (second tube 104) until the third tube 106 is reached. When in the third tube 106, and in particular, the third layer 44 of the third tube 106, dissection proceeds circumferentially until the dissection meets the posterior dissection. The simulated mesorectum (second tube 104) has an area of reduced thickness and the third tube 106 is attached to the second tube 104 and indistinguishably colored when comparing the yellow first layer 32 with the yellow second tube 104. The simulated prostate system 110 is located on top of the third tube 106 as shown in FIG. 7 and it is surrounded with polyfill fiber 112 which makes it harder to distinguish from the polyfill fiber of the third layer 44 of the third tube 106 while dissecting in the third tube 106. Dissection proceeds until the pelvic cavity is breached.

The proximal end of the simulated rectum model 100 may be attached to a transanal adapter. The transanal adapter is a leg 20 used to space apart the top cover 16 from the base 18 of a surgical trainer 10 to provide access into the model 100 from the side of the surgical trainer. The transanal adapter includes an opening that is connected to the first lumen 103 of the first tube 102. Surrounding the opening of the transanal adapter, soft silicone is provided to simulate an anus. The practice of the surgical TaTME procedure is performed through the opening of the transanal adapter with a circumferential purse string suture placed proximal to the transanal adapter with the simulated prostate system located distal to the transanal adapter.

The simulated rectum model 100 is manufactured by first placing a mesh sheath on a mandrel and paining uncured silicone over the mesh. The second tube 104 (simulated mesorectum) is made of urethane foam that is cast into a flat sheet. The foam is cast to have a thinner section. The simulated mesorectum is wrapped into a cylinder around the first tube 102 to create the second tube 104. Cyanoacrylate glue is used together with a primer to adhere the thicker portions of the second tube 104 together on the posterior side of the simulated rectum 100. To form the third tube 106, a thin planar sheet of yellow silicone is cast onto foam to create the first layer 32. While the silicone of the first layer 32 is still wet, a layer of polyfill is evenly placed on top to create the third layer 44 of polyfill. After the first layer 32 cures, it is de-molded. A new layer of white-colored or clear silicone is cast on the foam to form the second layer 34. The previously-cured first layer 32 together with the polyfill third layer 44 is placed on top with the polyfill third layer 44 touching the wet silicone of the second layer 34. The assembly is demolded and wrapped around the second tube 104 to form a cylindrical third tube 106 which is adhered to the second tube 104 using cyanoacrylate glue. The fourth tube 108 is formed in a similar fashion as the third tube 106.

To form the fourth tube 108, a thin planar sheet of white or clear silicone is cast onto foam to create the first layer 32. While the silicone of the first layer 32 is still wet, a layer of polyfill is evenly placed on top to create the third layer 44 of polyfill. More polyfill fiber is added to create an area where the third layer 44 is thicker as shown in FIG. 7 . After the first layer 32 cures, the third layer 44 is adhered and the combination of the first layer 32 and the third layer 44 is de-molded. A new layer of red-colored silicone is cast on the foam to form the second layer 34 of the fourth tube 108. The previously-cured first layer 32 together with the polyfill third layer 44 is placed on top with the polyfill third layer 44 touching the wet silicone of the second layer 34. Once cured, the assembly is demolded and wrapped around the third tube 106 to form a cylindrical fourth tube 108 which is adhered to the third tube 106 using cyanoacrylate glue or silicone dots. The simulated prostate system 110 is previously formed and located between the third tube 106 and the fourth tube 108.

Turning now to FIG. 9A, there is shown a casting dish 52 that has a textured molding surface. The surface may vary in thickness. A first layer 32 of uncured silicone is poured into the casting dish 52. Before it is allowed to cure, a third layer 44 a of fiber is placed on top of the first layer 32 such that fibers on one side of the third layer 44 a are embedded into the first layer 32. The first layer 32 is allowed to cure. After curing, the first layer 32 is removed from the casting dish 52 with the help of the third layer 44 a. The third layer 44 a and the first layer 32 are pulled up from the casting dish 52. Because the third layer 44 a adhered to the first layer 32, pulling up on the third layer 44 a allows the fibers of the third layer 44 a to distribute the removal force and advantageously prevent the thin first layer 32 from tearing during removal. After the combination of the first layer 32 and the third layer 44 a is removed, it is inverted and placed in juxtaposition to a second casting dish 52 with a second layer 34 of wet silicone as shown in FIG. 9B. Another third layer 44 b of fiber is placed onto the second layer 32 of wet silicone. Inclusions 48 are placed over the third layer 44 b. Part of the inclusions 48 are placed in contact with the second layer 34 and remains embedded in the second layer 34 when the second layer 34 finishes curing. The third layer 44 b also is embedded into the second layer 34. In one variation, the inclusions 48 are not embedded in the second layer 34 and are located between the third layers 44 a, 44 b. When the first layer 32 with the first third layer 44 a are placed over the second layer 34, the inclusions 48 and the second third layer 44 b, the construct is completed. In another variation, the first layer 32 is placed into contact with the second layer 34 while the second layer 34 is still uncured to adhere the first layer 32 and create a pocket that includes the inclusions 48 and third layers 44 a, 44 b. In another variation, portions of the third layer 44 a are also embedded into the second layer 34 while the silicone is still wet to embed the third layer 44 a into the second layer 34. The inclusions 48 shown in FIG. 9B are vasculature made of silicone; however, the invention is not so limited and the inclusions 48 may be any inclusion, anatomical structure, landmark, organ, nerves, tissue, tumors and the like.

Turning now to FIGS. 10-11 with particular reference to FIGS. 10A-10B, there is shown a casting dish 52 having two channels 72 for receiving uncured silicone. Although two channels 72 are shown any pattern can be employed to receive uncured material and form a desired structure including but not limited to anatomical structures and landmarks, tissues, nerves, vasculature, tumors, organs and the like. The material may include uncured silicone, uncured urethane foam, uncured silicone foam and the like. In one variation, wet uncured urethane foam is poured into the channels 72 to create a first inclusion 48 a as shown in FIG. 11A. A first fiber layer 44 a is placed on top of the uncured foam 48 a inside the channels 72 to embed the fiber layer 44 a into the uncured foam. The uncured silicone inside the channels 72 is allowed to cure and as a result become attached to the first fiber layer 44 a. The first fiber layer 44 a together with the formed inclusions 48 a are removed from the casting dish 52 and placed in juxtaposition to a first layer 32 of uncured silicone as shown in FIG. 11B. The first fiber layer 44 a with the attached first inclusions 48 a are pressed into the first layer 32 while the silicone is still wet to embed the first inclusions 48 a and the first fiber layer 44 a into the first layer 32 as shown in FIG. 11C. The first inclusions 48 a are configured to depict and mimic nerves; however, the first inclusions 48 a can be any type of inclusion suitable for the simulated tissue structure. A second fiber layer 44 b made of fiber is provided together with one or more second inclusion 48 b. The second inclusions 48 b are attached to the second fiber layer 44 b in the same manner as described above with respect to the first fiber layer 44 a and first inclusions 48 a and may be made of silicone, silicone foam, urethane foam and the like. A casting dish is provided that is configured with a pattern for molding the one or more second inclusion 48 b. The pattern is filled with wet silicone, for example, and while uncured, the second fiber layer 44 b is overlaid onto the casting dish and wet silicone of the second inclusions 48 b to embed and attach the second inclusions 48 b to the second fiber layer 44 b along a first side of the second fiber layer 44 b. The second side of the second fiber layer 44 b is embedded into a second layer 34 while the second layer 34 is still uncured. When the second inclusions 48 b and the second layer 34 are cured the second fiber layer 44 b and the second layer 34 together with the second inclusions 48 b are removed from the respective casting dishes and placed on the first fiber layer 44 a, first layer 32 and first inclusions 48 a to create the sandwich-like simulated tissue construct. The second inclusions 48 b are configured to mimic vasculature or any other anatomical structure, tissue, organ, nerve, tumor and the like. One or more of the first fiber layer 44 a and second fiber layer 44 b, create ideal dissection pathways for skeletonizing any one or more of the inclusions 48 a, 48 b wherein the dissection pathway through the fiber creates a realistic look and feel with the fibers being capable of being cut and/or spread apart to separate and expose the layers and inclusions for removal.

Any portion of the model 30 can be made of one or more organic base polymer including but not limited to hydrogel, single-polymer hydrogel, multi-polymer hydrogel, rubber, latex, nitrile, protein, gelatin, collagen, soy, non-organic base polymer such as thermo plastic elastomer, Kraton, silicone, foam, silicone-based foam, urethane-based foam and ethylene vinyl acetate foam and the like. Into any base polymer one or more filler may be employed such as a fabric, woven or non-woven fiber, polyester, non-absorbent fiber, nylon, mesh, cotton and silk, conductive filler material such as graphite, platinum, silver, gold, copper, miscellaneous additives, gels, oil, cornstarch, glass, dolomite, carbonate mineral, alcohol, deadener, silicone oil, pigment, foam, poloxamer, collagen, gelatin and the like. The adhesives employed may include but are not limited to cyanoacrylate, silicone, epoxy, spray adhesive, rubber adhesive and the like.

It is understood that various modifications may be made to the embodiments and variations disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the present disclosure. 

We claim:
 1. A simulated tissue structure for surgical training, comprising: a first layer of silicone polymer with an upper surface and a lower surface defining a thickness therebetween; a second layer of silicone polymer with an upper surface and lower surface defining a thickness therebetween; the second layer being spaced apart from the first layer defining a gap therebetween such that the upper surface of the first layer faces the lower surface of the second layer; an inclusion located between the first layer and the second layer; and a third layer made of a plurality of entangled fibers located between the first layer and the second layer; the plurality of entangled fibers residing within the gap in a randomly arranged fashion such that part of the plurality of entangled fibers is embedded in both the first layer and second layer to create a mechanical linkage of fiber connecting the first layer and the second layer, thereby providing a dissection plane for practicing surgical excision of the inclusion.
 2. The simulated tissue structure of claim 1 wherein the third layer is made of polyester fiber.
 3. The simulated tissue structure of claim 1 wherein the inclusion is adhered to or embedded in at least one of the first layer and the second layer.
 4. The simulated tissue structure of claim 1 wherein the inclusion is selected from the group consisting of simulated anatomical structure, organ, vasculature, nerve, tissue, tumor, prostate, prostate system, vein, vessel, and lumen.
 5. The simulated tissue structure of claim 1 wherein each of the plurality of entangled fibers is in the form of a strand, filament, yarn, or micro-fiber having a length and a first free end and a second free end.
 6. The simulated tissue structure of claim 5 wherein some strands of fiber are embedded into the first and second layers at one or more locations along the length of the fiber while their first and second free ends may or may not be embedded in the first or second layers; some other strands of fiber being freely disposed between the first layer and second layer without being embedded in the first layer or the second layer, yet other strands of fiber being entangled and intertwined with other strands of fiber in a loose fashion so as to be able to move relative to the other strands of fiber.
 7. The simulated tissue structure of claim 1 wherein the plurality of entangled fibers are selected from a group consisting of polyester, polyamide, acrylic, acetate, polyolefin, cotton, fiberfill, batting, polyethylene terephthalate, polyethylene naphthalate, nylon, polyfill, polymer, plastic, spandex, natural fiber, non-absorbent fiber, and synthetic fiber.
 8. The simulated tissue structure of claim 1 wherein the third layer has a thickness within a range of about 2.5 mm to 25 mm.
 9. The simulated tissue structure of claim 1 wherein the thickness of the first layer and the second layer are within a range of about 1 mm to 7 mm.
 10. The simulated tissue structure of claim 9 wherein the thickness of the first layer and the second layer are preferably within a range of about 0.5 mm to 3 mm.
 11. The simulated tissue structure of claim 1 wherein the thickness of the first layer and second layer are the same or different.
 12. The simulated tissue structure of claim 1 wherein the thickness of each of the first and second layers is substantially uniform between their respective upper surfaces and lower surfaces defining a substantially planar configuration.
 13. The simulated tissue structure of claim 1 wherein both of the first and second layers are having locations of reduced thickness where the plurality of entangled fibers are embedded in one of the first layer and the second layer.
 14. The simulated tissue structure of claim 13 wherein the locations of reduced thickness on the first and second layers are isolated spots acting as points of origin for tears in the first and second layers to mimic real dissection.
 15. The simulated tissue structure of claim 1 wherein perimeter areas of the first and second layers are sealed together to create a sealed pocket of fibers.
 16. The simulated tissue structure of claim 15 wherein the perimeters areas of the first and second layers are configured to have no third layer.
 17. The simulated tissue structure of claim 1 wherein part of the third layer which is adjacent to the first layer and part of the third layer which is adjacent to the second layer comprises fiber strands coated in silicone.
 18. The simulated tissue structure of claim 1 wherein the plurality of entangled fibers of the third layer act as an adhesive layer of fiber between the first layer and second layer.
 19. The simulated tissue structure of claim 18 wherein the adhesion between the first and second layers is defined by the plurality of entangled fibers and their degree of adhesion to the first and second layer.
 20. The simulated tissue structure of claim 1 wherein the plurality of entangled fibers of the third layer are arranged in a desired density, shape and thickness. 